The present invention relates to ultra-high molecular weight poly(vinyl acetate) and ultra-high molecular weight poly(vinyl alcohol). Poly(vinyl acetate) and poly(vinyl alcohol) produced in accordance with this invention have an essentially linear polymeric backbone. Additionally, the invention includes a novel process for production of the ultra-high molecular weight polymers.
Poly(vinyl alcohol) is conventionally produced in a two step process. The initial step comprises polymerizing vinyl acetate to produce poly(vinyl acetate). The second step comprises subjecting the poly(vinyl acetate) to alcoholysis (methanolysis or ethanolysis) in order to convert the poly(vinyl acetate) to poly(vinyl alcohol).
Canadian Pat. No. 663,529 discloses essentially linear poly(vinyl acetate) having an intrinsic viscosity of 1.7 to 3.2 dL/g. Accordingly, based upon numerical calculations, the poly(vinyl acetate) of Canadian Pat. No. 663,529 has a viscosity average molecular weight ranging from about 640,000 to about 1,500,000. Alcoholysis of the poly(vinyl acetate) of Canadian Pat. No. 663,529 would produce poly(vinyl alcohol) having a viscosity average molecular weight ranging from about 327,000 to about 765,000.
United Kingdom Pat. No. 900,571 discloses poly(vinyl alcohol) having the molecular structure ##STR1## where n is the average degree of polymerization with n being 4,700. The poly(vinyl alcohol) of United Kingdom Pat. No. 900,571 has a viscosity average molecular weight of about 202,000, and the corresponding poly(vinyl acetate) of United Kingdom Pat. No. 900,571 has a viscosity average molecular weight of about 404,000.
Some investigators indicate that production of essentially linear poly(vinyl acetate) requires a polymerization temperature below about -15.degree. C. Atkinson et al., European Polymer Journal, Vol. 15 pp 21-26 (1979); Hobbs et al., Journal of Polymer Science, Vol. XXII, pp. 123-135, 124 (1956); Burnett et al., Journal of Polymer Science, Vol. XVI, pp. 31-44, 39 (1955). Hobbs et al. disclose at page 125 the preparation of an essentially linear poly(vinyl acetate) having an intrinsic viscosity of 3.11. In order to produce this polymer, Hobbs et al. employed azobisisobutyronitrile as an initiator at a concentration of 2.33.times.10.sup.-4 moles per liter and allowed the polymerization to continue for 37.5 hours at a temperature of -19.degree. C.
Burnett et al. found that a polymerization temperature of -25.degree. C. to -38.degree. C. could be employed in order to obtain essentially linear poly(vinyl acetate). However, Burnett et al. noted that polymers prepared at -38.degree. C. had essentially the same molecular shape as those prepared at -25.degree. C. A contrary view is that the polymerization temperature is irrelevant and that essentially linear poly(vinyl acetate) may be obtained as long as the polymerization is not allowed to proceed to high conversions of the monomeric vinyl acetate. Matsumoto et al., Journal of Polymer Science, Vol. XLVI pp. 520-523 (1960).
Is is generally agreed that conversion of the monomer should be limited. This can be accomplished by controlling polymerization time, light intensity, initiator concentration and polymerization temperature. However, an optimum combination of these parameters is not known. Accordingly, one of the objects of the present invention is to provide a photoinitiated process for the production of essentially linear ultra-high molecular weight poly(vinyl acetate) which includes a novel combination of initiator concentration, polymerization temperature and length of polymerization time.